Exodus 7:22-25

But the magicians of Egypt did the same with their secret arts; and Pharaoh’s heart was hardened, and he did not listen to them, as the LORD had said. Then Pharaoh turned and went into his house with no concern even for this. So all the Egyptians dug around the Nile for water to drink, for they could not drink of the water of the Nile. Seven days passed after the LORD had struck the Nile.